1 files changed, 40 insertions, 0 deletions
diff --git a/tools/get-scala-commit-drift b/tools/get-scala-commit-drift
new file mode 100755
index 0000000000..4959826ec1
--- /dev/null
+++ b/tools/get-scala-commit-drift
@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+#
+# Usage: get-scala-commit-drift [dir]
+# Figures out current commit drift of a git clone.
+# If no dir is given, current working dir is used.
+#
+# Example output string:
+#   123
+#
+# Build drift = # of commits since last tag.
+
+[[ $# -eq 0 ]] || cd "$1"
+
+ensure_tag () {
+  sha=$1
+  rev=$2
+  
+  [[ -n $(git tag -l $rev) ]] || {
+    git tag -a -m "generated by get-scala-revision" $rev $sha
+  }
+}
+
+# Ensure some baseline tags are present so if this repository's
+# tags are screwed up or stale, we should still have a reference
+# point for a build string.
+ensure_tag 58cb15c40d v2.10.0-M1
+ensure_tag 29f3eace1e v2.9.1
+ensure_tag b0d78f6b9c v2.8.2
+
+# the closest tag, obtained separately because we have to
+# reconstruct the string around the padded distance.
+tag=$(git describe --tags --match 'v2*' --abbrev=0)
+
+# printf %016s is not portable for 0-padding, has to be a digit.
+# so we're stuck disassembling it.
+described=$(git describe --tags --match 'v2*' --abbrev=10)
+suffix="${described##${tag}-}"
+counter=$(echo $suffix | cut -d - -f 1)
+
+echo "$counter"